This invention pertains to microbe inhibitors and particularly to the use of quaternary ammonium salts applied on a substrate as inhibitors of microbial growth, and to the preparation thereof.
Water based polymer emulsions (such as latex emulsions) are susceptible to microbial contamination resulting in product spoilage. Polymer emulsions are dispersions of fine organic polymer particles in water. These polymer particles are suspended and stabilized in an aqueous environment with additional organic substrates, such as surfactants and protective colloids. Surfactants, protective colloids, such as poly(vinyl alcohol) and hydroxyethyl cellulose, thickeners and other additives, and the polymer itself all provide a supply of carbon nutrition for microorganisms to metabolize. Polymer emulsions are therefore susceptible to spoilage due to microbial attack and propagation.
One problematic microbe is mold. Mold is a term used to describe a type of fungus that typically grows on the surface of organic matter. More specifically, mold or fungus is a eukaryotic organism that digests its food externally and absorbs the nutrient molecules into its cells. Growth of mold on the surface of wallboard paper or in or on gypsum containing a carbohydrate source transpires when a spore comes into contact with the nutritional matrix. Mold growth ensues if the environmental and biological conditions are right. Initially, there is spore germination, then formation of hyphal growth, followed by spore formation and spore dispersion. In general, mold will not grow on the core component of wallboard. However, if a starch is added then nutrients are present and mold will grow if the gypsum matrix becomes wet and is exposed to mold spores.
Standard industrial practices combat such product biodeterioration by the addition of various industrial biocides (i.e. antimicrobial agents) directly after the manufacturing process. Examples of commonly used industrial biocides are: 1,2-benzisothiazolin-3-one (“BIT”), and a blend of 5-chloro-2-methyl-4-isothiazolin-3-one (“CIT”) and 2-methyl-4-isothiazolin-3-one (“MIT”). Examples of other biocides commonly used for polymer emulsion preservation include 1,2-dibromo-2,4-dicyanobutane (“DBDCB”), 2,2-dibromo-3-nitrilopropionamide (“DBNPA”), 2-bromo-2-nitro-1,3-propanediol (“BNPD”), aldehyde derivatives, formaldehyde releasing agents, hydantoins, chlorinated aromatics, 2-(Thiocyanomethylthio)benzothiazole (CAS 6441-45-8, sold as Busan® and other names), Microban® (U.S. Pat. No. 6,767,647), and salt of pyrithione (U.S. Pat. No. 6,893,752).
These commonly used biocides are usually adequate to preserve various types of polymer emulsions against most industrial spoilage from bacteria and fungi. However, polymer emulsions stabilized with protective colloids, such as poly(vinyl alcohol) or hydroxyethyl cellulose, and/or nonionic surfactants, pose additional strains and challenges to many preservative systems. In general, it has been found that this class of polymer emulsion products is more susceptible to spoilage than other polymer emulsions by certain types of microbes. For example, biodeteriogenic microbes that can survive in acidic environments and/or that metabolize alcohols, such as Gluconoacetobacter liquefaciens (“GABL”), have begun to emerge and thrive in polymer emulsions, even in the presence of commonly used industrial biocides. Biodeteriogenic microbes include bacteria and fungi that can adversely affect the commercial value of products and materials. Some biodeteriogenic microbes have become so well adapted to the environment present in these emulsions, such as poly(vinyl alcohol)-stabilized poly(vinyl acetate-co-ethylene) copolymer emulsions, that the standard industrial biocides are inadequate to prevent product spoilage by this species over the entire product shelf life period; e.g., 6 to 12 months. A significant rise in polymer emulsion biodeterioration problems has resulted in a need to identify more effective preservative systems.
It is known that volatile organic compounds (VOC's″), such as unreacted monomers, in polymer emulsions exert some level of a bacteriostatic, if not bacteriocidal, effect, which can inhibit the growth of biodeteriogenic microbes. Recent developments in polymer emulsion technology, in response to regulatory issues and environmental concerns, have led to reductions in residual VOC and residual monomer levels. Such VOC reductions impact polymer emulsions in many ways. For example: (1) they create an emulsion environment more conducive to microbial growth, (2) they may permit the emergence of new microorganisms that find the new emulsion environment more hospitable, (3) they pose additional challenges to current preservative technologies, and (4) they create the need for new preservation methods to prevent biodeterioration over the products shelf life.
Although there are a significant number of biocides that can kill microorganisms effectively and can provide very good preservation for polymer emulsions and other industrial products, only a limited number of these exhibit acceptably low toxicity to higher organisms, e.g., humans. The choice of effective biocides that can be added to polymer emulsions becomes even more limited when United States Food and Drug Administration (“FDA”) clearances are required for the polymer emulsion end use. Many polymer emulsions are used to manufacture consumer goods, such as adhesives and papers for food packaging, diapers, paper towels, baby wipes, and feminine hygiene products. As a result of such contact with skin and indirect contact with foods, the polymer emulsions used in these applications must have the appropriate FDA clearances. These FDA clearances are based on favorable toxicological profiles, including no skin sensitization. In order for a polymer emulsion to receive the necessary FDA clearances, all of its constituents, including the preservative technology, must meet the FDA's rigorous toxicological criteria when used at concentrations required for satisfactory performance in the polymer emulsion. FDA-approved biocides have use level restrictions. In some cases, the minimum biologically effective concentration is greater than the maximum allowable use level. Typically, this results in premature product biocontamination and biodeterioration. Additionally, microorganisms continue to evolve and new microorganisms are beginning to appear that exhibit resistance to some of the more common industrial biocidal agents, particularly at the allowable use level. A tightening regulatory environment, specific consumer good manufacturing specifications, public concern, and product liability, further complicate biocide selection and use. For example, isothiazolinones are widely used antimicrobial agents for many consumer products, but their known skin sensitization property causes concern among many consumer goods manufacturers. Such health concerns and microbial resistance are leading to a search for preservation alternatives and new preservation approaches.
Cationic compounds, such as quaternary ammonium compounds, are well known in the antimicrobial art and are widely used as disinfectants for surfaces. For example, they are used to disinfect floors, walls, countertops, equipment surfaces, food contact surfaces, and the like in hospitals, schools, nursing homes, restaurants, and residential homes. Furthermore, combinations of detergents with cationic compounds are widely used formulations for cleaning and disinfecting or sanitizing such surfaces with a single product. Cationic compounds are also used to inhibit the growth of algae and microorganisms in water, such as in swimming pools. Cationic compounds have been utilized on a limited basis for the preservation of industrial products and to prevent microbial growth in aqueous systems.
Cationic compounds, such as quaternary ammonium compounds, are usually prepared by the reaction between an amine and a suitable electrophile. Suitable electrophiles that have been used include alkyl halides and substituted epoxides.
Great Britain Patent No. 1,091,049 (1967) discloses the preparation of bacteriostatic tissue paper by incorporating alkylated guanidine salts during the tissue paper manufacturing process. The guanidine salt is introduced into the paper pulp slurry prior to sheet formation.
U.S. Pat. No. 3,970,755 (Gazzard et al., 1976) discloses biocidal compositions for aqueous systems comprising lauryl benzyl dimethyl ammonium chloride or cetyl trimethyl ammonium chloride, and 1,2-benzoisothiazolin-3-ones.
U.S. Pat. No. 4,661,503 (Martinet al., 1987) discloses a synergistic biocide composition of n-dodecylguanidine hydrochloride (“DGH”) and a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one for treating industrial process waters to prevent the growth of gram negative bacteria and fungi.
U.S. Pat. No. 4,725,623 (Whitekettle et al., 1988) discloses a bactericidal composition for aqueous systems comprising a synergistic aqueous mixture of 2-bromo-2-nitropropane-1,3-diol and n-dodecylguanidine.
U.S. Pat. No. 4,906,385 (Lyons, et al., 1990) discloses the use of water soluble C8-C18 alkyl guanidine salts, especially n-dodecylguanidine hydrochloride, for controlling macroinvertebrate biofouling of industrial cooling water system.
U.S. Pat. No. 5,041,463 (Whitekettle et al., 1991) discloses a bactericidal composition for aqueous systems, such as pulp and paper mill systems, comprising a combination of glutaraldehyde and dodecylguanidine hydrochloride.
U.S. Pat. No. 5,457,083 (Muia et al., 1995) discloses synergistic antimicrobial compositions containing polyether polyamino methylene phosphonates (“PAPEMP”) and one or more non-oxidizing biocide, such as didecyl dimethyl ammonium chloride, dodecylguanidine hydrochloride, methylene bisthiocyanate, and 5-chloro-2-methyl-4-isothiazolin-3-one. The combination is reported to be useful in aqueous systems in a variety of industrial applications, such as papermaking, paints, adhesives, latex emulsions, and joint cements. Examples show that addition of PAPEMP to a non-oxidizing biocide improves bacterial kills in an aqueous system over 24 hour period.
U.S. Pat. No. 6,680,127 (Capps, 2004) describes a gypsum board having antifungal properties obtained through the addition of a controlled-release antifungal agent. The agent is cetylpyridinium chloride (“CPC”), which is a relatively small molecule having a relatively large alkyl side chain (C=16). The use of this relatively small molecule is ideal for this technology because the CPC is mixed with the gypsum powder in water to create the gypsum board, and molecules with longer alkyl side chains have reduced solubility in water. In addition, the patented gypsum board possesses a relatively large quantity of CPC, on the order of 0.01 to 1.5 weight percent of the dry weight of the gypsum in the board. The patented gypsum board also includes one or more encapsulators, binders, and retention aids. The retention aids used in the gypsum board include cationic, anionic and nonionic surfactants, polyacrylamides, polyamines, polyethyleneimines, cellulosic ethers, aldohexoses, starch, and combinations thereof.
U.S. Pat. No. 6,890,969 (Rabasco et al., 2005) describes compositions containing colloid-stabilized polymer emulsions and cationic compounds that are resistant to contamination with biodeteriogenic microbes. Examples of suitable microbicidal cationic compounds are: substituted pyridinium salts, substituted guanidine salts, tetrasubstituted ammonium salts, and polymeric cationic compounds.
U.S. Patent Publication No. 20040033343 pertains to mold-resistant corrugated cardboard that can be used in home construction. The cardboard includes liners which are infused with biocides such as 5-chloro-2-methyl-4-isothiazolin-3-one, hypochlorite and sodium hydroxide and sodium bromide. An additional medium between the liners can also include the biocides 1,2-benzothiazol-3(2H)-one and poly[oxyethylene(dimethyliminio)ethylene dichloride].
El-Zayat and Omran, “Disinfectants Effect on the Growth and Metabolism of Acetobacter aceti” (Egypt J-Food-Sci., 11(1-2), 1983, pages 123-128) evaluates quaternary ammonium compounds, such as cetyl trimethylammonium bromide, as disinfectants against the growth and metabolism of Acetobacter aceti. 
Handbook of Biocide and Preservative Use, Edited by H. W. Brancq and Boiteux, Rossmore, Blackie Academic & Professional, 1995, pages 361-362, describes biocidal surfactants for preservation of cosmetics and toiletries. Quaternary amines are reported to be potent antimicrobial substances.
U.S. Pat. No. 6,664,224 (Kourai, et al., 2003) discloses a method for the preparation of quaternary ammonium salts by the reaction between a tertiary amine and an U.S. Pat. No. 5,561,187 alkyl halide (chloride, bromide or iodide).
U.S. Pat. No. 6,414,159 (Sano, et al., 2002) discloses a method for the preparation of a quaternary ammonium halide by the reaction between a pyridine or N-alkylimidazole with an alkyl halide at high temperature.
U.S. Pat. No. 5,508,454 (Brancq and Boiteux, 1996) discloses a method for the preparation of a complex quaternary ammonium cation by alkylation of a tertiary amine with sodium chloroacetate.
U.S. Pat. No. 5,561,187 (Bechara and Baranowski, 1996) discloses a method for the preparation of a quaternary ammonium cation with two hydroxylated side chains by the acid-catalyzed reaction between a (hydroxyalkyl)dialkylamine and an epoxide.
U.S. Pat. No. 6,767,647 (Swofford et al., 2004) discloses a wallboard with antimicrobial characteristics. The wallboard may contain sodium pyrithione.
U.S. Pat. No. 6,893,752 (Veeramasuneni et al., 2005) discloses a gypsum panel that may contain a water-soluble pyrithione salt.
A need remains for a method of protecting polymer emulsions, especially those stabilized with hydroxyl-containing protective colloids and those with low VOC's, against product biodeterioration by microbes. There is also a need for polymer emulsion compositions which are resistant to biodeterioration over their shelf life (about 6 to 12 months).
Further, a need remains for a cost-effective method for the preparation of quaternary ammonium salts directly from alcohol precursors.